Institute of Botany, Faculty of Biology, Jagiellonian University, Gronostajowa 3, 30-387, Kraków, Poland.
Research laboratory 'Herbarium', National Research Tomsk State University, Lenin 36 Ave., 634050, Tomsk, Russia.
BMC Plant Biol. 2021 Nov 1;21(1):505. doi: 10.1186/s12870-021-03287-w.
The proper identification of feather grasses in nature is often limited due to phenotypic variability and high morphological similarity between many species. Among plausible factors influencing this issue are hybridisation and introgression recently detected in the genus. Nonetheless, to date, only a bounded set of taxa have been investigated using integrative taxonomy combining morphological and molecular data. Here, we report the first large-scale study on five feather grass species across several hybrid zones in Russia and Central Asia. In total, 302 specimens were sampled in the field and classified based on the current descriptions of these taxa. They were then genotyped with high density genome-wide markers and measured based on a set of morphological characters to delimitate species and assess levels of hybridisation and introgression. Moreover, we tested species for past introgression and estimated divergence times between them.
Our findings demonstrated that 250 specimens represent five distinct species: S. baicalensis, S. capillata, S. glareosa, S. grandis and S. krylovii. The remaining 52 individuals provided evidence for extensive hybridisation between S. capillata and S. baicalensis, S. capillata and S. krylovii, S. baicalensis and S. krylovii, as well as to a lesser extent between S. grandis and S. krylovii, S. grandis and S. baicalensis. We detected past reticulation events between S. baicalensis, S. krylovii, S. grandis and inferred that diversification within species S. capillata, S. baicalensis, S. krylovii and S. grandis started ca. 130-96 kya. In addition, the assessment of genetic population structure revealed signs of contemporary gene flow between populations across species from the section Leiostipa, despite significant geographical distances between some of them. Lastly, we concluded that only 5 out of 52 hybrid taxa were properly identified solely based on morphology.
Our results support the hypothesis that hybridisation is an important mechanism driving evolution in Stipa. As an outcome, this phenomenon complicates identification of hybrid taxa in the field using morphological characters alone. Thus, integrative taxonomy seems to be the only reliable way to properly resolve the phylogenetic issue of Stipa. Moreover, we believe that feather grasses may be a suitable genus to study hybridisation and introgression events in nature.
由于许多物种之间存在表型变异性和高度的形态相似性，因此在自然界中正确识别羽毛草往往受到限制。影响这一问题的合理因素包括最近在该属中检测到的杂交和基因渐渗。尽管如此，迄今为止，只有一组有限的分类单元使用结合形态和分子数据的综合分类学进行了调查。在这里，我们报告了首次对俄罗斯和中亚几个杂交区的五种羽毛草种进行的大规模研究。总共在野外采集了 302 个标本，并根据这些分类单元的当前描述进行了分类。然后，他们用高密度的全基因组标记进行基因分型，并根据一组形态特征进行测量，以划定物种界限，并评估杂交和基因渐渗的水平。此外，我们还测试了物种的过去基因渐渗情况，并估计了它们之间的分歧时间。
我们的研究结果表明，250 个标本代表五个不同的物种：S. baicalensis、S. capillata、S. glareosa、S. grandis 和 S. krylovii。其余 52 个个体提供了 S. capillata 和 S. baicalensis、S. capillata 和 S. krylovii、S. baicalensis 和 S. krylovii 之间广泛杂交的证据，以及 S. grandis 和 S. krylovii、S. grandis 和 S. baicalensis 之间的杂交程度较小。我们检测到 S. baicalensis、S. krylovii、S. grandis 之间的过去网状进化事件，并推断 S. capillata、S. baicalensis、S. krylovii 和 S. grandis 内的物种多样化始于约 130-96 千年前。此外，遗传种群结构的评估显示，尽管一些物种之间存在显著的地理距离，但来自 Leiostipa 节的物种之间仍存在当代基因流的迹象。最后，我们得出结论，仅根据形态特征，只有 52 个杂交分类单元中的 5 个得到了正确识别。
我们的结果支持杂交是推动 Stipa 进化的重要机制的假设。因此，这种现象使得仅使用形态特征在野外识别杂交分类单元变得复杂。因此，综合分类学似乎是正确解决 Stipa 系统发育问题的唯一可靠方法。此外，我们认为羽毛草可能是研究自然杂交和基因渐渗事件的合适属。
